Preparation Of Metal Ion Pre-intercalation Vanadium Oxide And Its Application In Aqueous Zinc-ion Batteries

Rechargeable zinc ion batteries featuring intrinsic safety,environmental benignity,cost effectiveness,and high conductivity of aqueous system are regarded as high-potential grid energy storage systems.However,the developments of high-performance cathodes with large capacity,high energy density,and long-term cyclability remain a huge challenge,owing to sluggish Zn²⁺ions intercalation kinetics with bivalent charges in the cathodes.Layered vanadium-based materials can be promising cathodes for aqueous zinc ion batteries,owing to low cost,high abundance,high capacity with multi-electron transfer.However,Zn²⁺ion intercalation/deintercalation as well as structure partially dissolve in aqueous systems prevent the use of the durability.Herein,the“pillar”strategy through employing cations or lattice water in the layered vanadates has been proven to greatly enhance their rate performance and cycling stability.In this paper,hydrothermal reaction and solution immersion are used to realize the pre-intercalation of metal cations in vanadium oxide,aiming to improve structure stability of vanadium oxide during the cycle of aqueous zinc ion batteries.The main research contents are as follows:（1）Based on the hydrothermal reaction method,a novel heterostructure nanowire with Na V₆O₁₅ as the skin and V₂O₅ as the core was prepared using SDS and NH₄VO₃as precursor.By studying different hydrothermal time,the formation mechanism of the skin-core structured nanowire was clarified.At the same time,the electrochemical properties of the products obtained with different hydrothermal time were discussed,and then the contribution of Na V₆O₁₅ and V₂O₅ to the excellent Zn²⁺ions storage performance of the electrode material was studied.In this system,Na V₆O₁₅ is used to stabilize the structure of the active material,while V₂O₅is used to improve the specific capacity of the electrode.The obtained Na V₆O₁₅/V₂O₅ electrode material can maintain a specific capacity of 267 mAh g^-1 even after 3000 cycles at a current density of 5 A g^-1,showing the outstanding cycle stability of the electrode material.（2）Based on a simple solution immersion method,the V₂O₅ nanoparticles and alkali metal ion salt solution as precursor,after a long time of standing and subsequent calcination treatment,the pre-intercalation of alkali metal ions can be achieved.And the influence of different metal ion salt solutions on the morphology and structure transformation of vanadium oxide were systematically studied,and the pre-intercalation mechanism of alkali metal ions also was inferred.The intercalation rate of alkali metal ions decreases as the electronegativity of metal ions increases,and the morphology of the obtained nanomaterials is affected by the types of metal ions.At the same time,the changes in the structure of nanomaterials at different calcination temperatures and the effects on the storage of Zn²⁺ions are also compared.The results show that the presence of partially structure water is beneficial to improve the stability of the electrode material structure during cycling,The initial discharge specific capacity of LVO-200,NVO-300 and KVO-300 at 0.5 A g^-1 were 332,351 and 341 mAh g^-1,respectively,and the capacity retention rate after 100 cycles of cycling exceeded 90.10,96.40 and 91.17%,respectively.（3）Based on a simple solution immersion method,the V₂O₅ nanoparticles and alkaline earth metal ion salt solution as precursor,after a long time of standing and subsequent calcination treatment,the pre-intercalation of alkaline earth metal ions can be achieved.And the influence of different metal ion salt solutions on the morphology and structure transformation of vanadium oxide were systematically studied,and the pre-intercalation mechanism of alkaline earth metal ions also was inferred.Whether alkaline earth metal ions can successfully pre-intercalate vanadium oxide is closely related to its electronegativity.We have obtained the order of the recrystallization process in alkaline earth metal ion salt solution:Ca²⁺>Mg²⁺>Sr²⁺>Ba²⁺.Electrochemical performance studies have shown that the product obtained by pre-intercalation of Ca²⁺ions into vanadium oxide can be used as a candidate for the electrode of aqueous zinc ion batteries.Compared with other products,CVO-350exhibits high specific capacity,good rate performance and excellent cycle stability,and it can still maintain a high capacity retention rate of 87%at a high current density of 10A g^-1 after 2000 cycles.（4）Based on a simple solution immersion method,and V₂O₅ nanoparticles were soaked into the mixture salt solution of Na⁺ions and Ca²⁺ions.On the one hand,the vanadium oxides pre-intercalated with Na⁺ions and Ca²⁺ions both show good electrochemical performances.On the other hand,the Na⁺ions and Ca²⁺ions are located at the diagonal corners of adjacent main groups and exhibit similar physical and chemical properties.The results show that when the molar ratio of immersion solution is Na⁺:Ca²⁺=5:5 and the calcination temperature is 350℃,the synergistic effect of the pre-intercalated bimetallic ions can best promote the intercalation/extraction of Zn²⁺ions,and the outstanding cycle stability with a capacity retention close to 100%after200 cycles at 0.5 mA g^-1 can be achieved.